It will move to a purpose-built headquarters in the Jewellery Quarter, which will be completed by next year.
Established in 1773 by an Act of Parliament, the Assay Office Birmingham - one of only four in the country - currently employs around 120 staff who are responsible for the testing, verifying and hallmarking of several million articles of precious metal each year.
In recent years The Assay Office has diversified into other sectors and now provides a range of independent conformance testing for jewellery and fashion accessories as well as jewellery and watch valuations and gemstone verification.
Stella Layton, chief executive and Assay Master at the Birmingham Assay Office, said: "The completion of our new building on Icknield Street will allow our business to develop and diversify our range of services further and perform more efficiently, offering a better and safer facility for our employees and our customers.
"The new building will host our heritage silver collection and library, making this valuable resource more readily accessible to the trade, the public and those who wish to use it for educational and research purposes."